1. Field of the Invention
This invention relates to gas turbine engines and more particularly to structures for sealing between an array of stator vanes in a circumscribing engine case.
2. Description of the Prior Art
Gas turbine engines of the type to which the present invention applies principally comprise a compression section and a turbine section. In such engines a rotor assembly extends axially through the compression and turbine sections and is circumscribed by an engine case. Rows of rotor blades extend outwardly from the rotor in both the compression and the turbine sections. An array of stator vanes extends inwardly from the engine case at the upstream end of each blade row to direct the working medium gases of the engine to a preferred angle of entry into the downstream row of rotor blades. Leakage of working medium gases around the array of stator vanes, such as between the vane array and the engine case, degrades engine performance and is to be avoided.
Various approaches to the problem of avoiding leakage between each array of stator vanes and the engine case have been addressed in the prior art. In one typical engine structure described in U.S. Pat. No. 2,942,844 to Neate entitled "Turbine Nozzle", a metal braid is mounted in a channel between the outer case and the array of stator vanes.
In other engine structures, such as that illustrated in U.S. Pat. No. 3,807,891 to McDow et al entitled "Thermal Response Turbine Shroud", vanes and shrouds are aerodynamically loaded against each other during operation to control leakage around the arrays of vanes by eliminating axial gaps. As shown in U.S. Pat. No. 2,915,280 to Sonder entitled "Nozzle and Seal Assembly", an array of stator vanes is assembled into a unit and placed in the engine in one piece. U.S. Pat. No. 3,765,791 to Trappmann uses an annular piston and piston rings to seal a back pressure cavity. A tongue extends from an outer shroud ring to engage a groove in the piston to block leakage of the working medium in a downstream direction between the piston and the array of stator vanes.
In recent years the need to produce energy efficient machines has grown with increases in fuel costs and the scarcity of fuel supplies. Because the leakage of the working medium between an array of stator vanes and the outer case decreases engine efficiency, research efforts are still directed at developing effective seals therebetween.